Work

Temporal and Spatial Dynamics of Critical Shear Stress of Bedload Transport in Gravel‐Bed Rivers Under Variable Sediment Supply Conditions

Year: 2026

Type: article

Abstract: Understanding the temporal and spatial dynamics of critical shear stress τ c * is essential for predicting bedload transport rate in gravel‐bed rivers, especially under changing sediment supply conditions. This study conducted eight experimental runs using four sediment supply regimes and two feed textures to investigate how sediment supply history, including supply rate, magnitude, and texture, influences τ c * under non‐equilibrium conditions. The bedload transport rate, bed elevation, and sediment storage were measured with high temporal resolution, and τ c * was estimated using three classical bedload transport models and a slope‐dependent equation. The results show that τ c * is not constant, but varies dynamically with sediment input and bed adjustment. The higher the sediment supply rate and magnitude, the greater τ c *. Different variable sediment supply regimes would produce different τ c * trajectories, which are related to the specific experimental sequence of pre‐supply adjustment, variable sediment input, and post‐supply reorganization. Longitudinal differences also developed: localized deposition and bed slope steepening in the upstream reach caused τ c * values to be about 43% higher than those in the downstream reach. Grain selective transport further shaped system behavior: coarse gravels ( D 50 ‐ D 84 ) are preferentially stored while intermediate fractions ( D 16 ‐ D 50 ) are efficiently transported, generating counterclockwise hysteresis loops between sediment transport and storage. Overall, these findings demonstrate that τ c * should be treated as a dynamic parameter controlled by bed slope, sediment supply history, and bed surface adjustment. It also provides new insights for sediment transport modeling and river management under variable sediment regimes.

Source: Water Resources Research

DOI: 10.1029/2025wr043250